<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <h2>我是弹出子窗口</h2>
  <button id="popupbtn">向父窗口传递信息</button>
</body>
<script>
  let popupbtn = this.document.querySelector('#popupbtn')
  popupbtn.onclick = function (e) {
    window.opener.postMessage('我是popup_page子窗口的信息')
  }
</script>
</html>